The German Patent Application Publication No. 25 44 976 discloses an apparatus for determining the mass throughput of pourable material, as lime dust or fine ore. The measurement is based on the effective inertia force, i.e. Coriolis force, caused by moving mass particles hitting a rotating reference body, as a measuring wheel comprising a rotating disk bearing radially extending guiding blades thereon, the pourable material being hurled off essentially vertical in respect of the axis of rotation. Changes in the driving torque are used as measurement value for determining the mass throughput which at constant angular speed of the measuring wheel is directly proportional to the measured torque. For detecting torque changes the known apparatus uses the power consumption of the driving motor.
Similar apparatuses are known from the German Patent Application Publications No. 33 46 145 and No. 39 40 576, where instead of measuring the power consumption of the driving motor the latter is supported pivotally or rotationally, respectively, and the reaction torque is directed to a laterally arranged load cell. In operation of the known apparatuses it is assumed for pneumatically conveyed pourable material that the mass of the heavy phase of a mass flow is very large, as compared with the mass of the gas, usually air or a conveying gas, contained in the mass flow, such that the gas quantity may be disregarded when determining the mass based on changes in torque. In the above mentioned German Patent Application Publication No. 33 46 145 it is mentioned that for compensating the latter should be fed back and the same air quantity should be used all the time in order to minimize measuring errors. Furthermore, it is suggested to provide a cellular wheel sluice in order to prevent acceleration of an uncontrolled air flow by the measuring wheel.
Similar means have been suggested in the description of a similar mass throughput measuring apparatus in Kochsiek: Handbuch des Wagens, pp. 378 to 380, Verlag Vieweg, 1988. Again, it is indicated that undesired air flows through the mass throughput measuring apparatus should be avoided by an appropriate design, i.e. by incorporating cellular sluices, supply worms, or the like. However, this is not possible for pneumatic conveying systems.